One of the currently widely used plastic packages for two-lead semiconductor devices, such as diodes--particularly rectifiers (currents of up to about 1 A and reverse voltages of about 100 V to 2 kV)--varistors or thermistors, has the shape of a cylinder with leads projecting in the same axis. The semiconductor die or chip and the inner ends of its leads are hermetically embedded in the plastic, e.g., a thermoplastic or a thermosetting plastic, and thus protected against physical damage and chemical influences, such as the entrance of moisture.
In the fabrication of such semiconductor devices with a plastic package, the manufacture of the die, i.e., a semiconductor chip, starts with a semiconductor wafer on which several 100 to several 1000 identical dies or chips are fabricated, and the leads for the semiconductor device are designed as plug leads ("head leads"), i.e., leads having a thickened, e.g., upset, portion at one end, the "head". Between the two heads, the die is attached by soldering, for example.
To achieve a high throughput, a large number of untinned plug leads is fed into magazines, a die, i.e., a semiconductor chip, is positioned on each of the heads, and the heads of other plug leads fed into a further magazine are placed on the dies. In a furnace, each of the dies is then connected with its two associated plug leads by soldering. If the finished semiconductor device is to have a high reverse voltage, the soldered dies are etched and covred with a suitable plastic.
Next, the semiconductor devices are transferred into molds where they are embedded in plastic. Only then are the leads of the individual semiconductor devices tinned, which is done by barrel tinning to achieve a high throughput. Then, however, the leads, which are bent during the tinning process, must be axially aligned again in suitable straightening devices. Only then are they tested, taped, and lettered.
Conventional straightening devices have an hourly throughput of about 20,000 semiconductor devices. As the prices of semiconductor devices are still falling, this throughput rate is much too low if low-cost volume production is to be achieved.
Although the manufacturing process described is a well proved high-volume process, efforts are being made to modify it, particularly ith a view to further reducing the manufacturing costs, and to provide semiconductor devices which can be made at even lower cost.
Accordingly, the object of the invention as claimed is to provide a semiconductor device which has a plastic package that is of a different design than the hitherto widely used plastic packages to achieve a cost reduction. The design of the leads is to differ from the conversational design, too. In the method, the above-described step of straightening the leads is to be eliminated. The same applies to the tinning following the molding or embedding. It is also within the scope of the object of the invention to provide an apparatus with which a higher hourly throughput of semiconductor devices is attainable.
One of the fundamental ideas of the invention is to manufacture the plastic package, hitherto formed by embedding or molding the die, as a can-shaped housing in a separate step, which offers the advantage of greater freedom in the choice of the starting plastic and the temperatures and pressures to be used in the packaging process, for example, as to fill the can with a plastic compound, such as a cast resin, after insertion of the die.
Another fundamental idea of the invention is the completely different starting point for the manufacture of the leads, namely to form the latter from a wire unwinding from a spool, to pass this wire through a major part of the manufacturing stages unseparated, and to separate it into the individual semiconductor devices only after formation of the plastic package, i.e., the mounting of the cans.
The invention offers the following advantages. A low-cost plastic can be used for the cans. The presses for producing the can-shaped housing can be simpler in construction and, thus, smaller than the presses used so far. The need for the straightening device described is eliminated, so that a higher hourly throughput is possible. No polarity-determining device followed by a turnover device is necessary, so that the semiconductor devices can be taped in the same direction without the turnover device, since the dies can be brought from the semiconductor wafer to the positions between the leads with a predetermined polarity, which can be maintained until the taping takes place.